Detectors useful for sensing a voltage or current level indicative of the power output level at a amplifier are well known to those skilled in the art. Additionally, in the field of microwave transmission, micro-strip directional couplers are similarly well known. For example, a micro-strip directional coupler is as shown in U.S. Pat. No. 5,159,298. Further, microwave filters, impedance matching networks, and couplers are well known in the art as shown in Microwave Filters, Impedance-Matching Networks, and Coupling Structures. George L. Matthaei, Leo Young, and E. M. T. Jones; McGraw-Hill Book Company, New York; 1964, Library of Congress Catalog Card No. 64-7937.
The Detectors for measuring amplifier RF power, for example, may be coupled to an RF power output line through a microwave coupler as known by those skilled in the art. At microwave frequencies, the coupler may be a micro-strip coupler as shown in the above specified patent. Where the RF power is to be transmitted over a wideband of frequencies, the coupler may exhibit a transfer function varying over that wide frequency band. For example, where the coupler has the characteristics of a bandpass filter, the power out of the coupler at the coupler port may vary, with an increasing power transfer characteristic as frequencies advance in bandpass from the low end with one or more peaks in the center of the bandspread and then decreasing towards the upper end of the bandpass. A matching network may then be used to compensate for that frequency varying transfer function. The purpose of the matching network is to receive the frequency varying output of the coupler and by the additional effect of the matching network's transfer characteristic, produce as substantially a flat power to frequency output response as possible to a detection device such as a detector diode.
However, as the coupler transfer characteristic is non-linear, the power frequency transfer characteristic at the diode detector varies nonlinearly with frequency. This results from the difficulty of matching that nonlinear coupler characteristic. Accordingly, the final signal out such as a voltage in the case of the detector diode, varies from a true signal substantially indicative of the RF amplifier power out over the frequencies in the bandpass.